Radioactivity Exploration from the Arctic to the Antarctic. Part 2. Ymer-80 Expedition

Abstract Levels of natural radioactivity such as 222Rn (radon) and its long-lived daughters 210Pb and 210Po were measured. The radon gas was trapped on cooled charcoal filters and the long-lived daughter products sampled on fibre filters on a daily basis. In addition, short-lived progenies were followed continuously on the filters in order to achieve a time resolution of about one hour. The average 222Rn concentration in air measured during the Ymer-80 expedition in samples north of latitude 78.8 °N, was 33 ± 4 (one standard error) mBq.m-3 during Leg 1 (July-Aug.) , and 105.3 ± 8.3 mBq.m-3 during leg 2 (Aug-Sept.). During a two-week period of persistent polar winds, the mean radon concentration decreased to 19± 5 mBq.m-3. During July, August and September, the monthly average concentrations of 210Pb in air at positions north of 75 °N latitude were 31 ± 15, 89 ± 61 and 105± 57 μBq.m-3 respectively with a the grand average for all 3 months of 75 ± 28 μBq.m-3. An extensive radiochemistry program was also established to measure 134+137Cs and the trans- uranium elements 238+239+240Pu and 241Am in water, sediment and biota. The concentration of 137Cs in surface seawater along the Norwegian coast was quite constant about 157±7 Bq.m-3. At a latitude about 72 oN it stat do decrease exponentially at a rate of 0.43 deg.-1 to about 20 ± 10 Bq.m-3 above 78 oN. The results of 137Cs in sediments indicate that the total integrated area-content of 137Cs in a 1000 m water-column and sediment is about 12 kBq.m-2. In biota, the highest activity concentration of 137Cs about 1000 Bq/kgdwt was found in lichens. The activity concentration of 137Cs in polar bears was about 10 Bq/kgdwt, in seals about 1 Bq/kgdwt, and in birds about 1-7 Bq/kgdwt. The activity-concentration of 137Cs in Fucus and Laminaria was about 1-2 Bq/kgdwt, and the algae/sea-water activity-concentration ratio was about 75. The distribution of the trans-uranium element 239+240Pu in sea water decrease from 14 to 10 mBq.m-3 up to 73°N but increase again to 17 mBq.m-3 at high latitudes while 137Cs decrease. The average 241Am/ 239+240Pu activity ratio was found to be 0.13 ±0.04 (2 S.E), of 31 samples with the range 0.04 - 0.32 in surface water, Deep-water samples have been sampled at latitudes around 80.4 ±1.4 °N and along longitudes 2° W – 45.5 °E. The results of the salinity and activity concentration of 137Cs and 239+240Pu with depth of water are indicate an exponential decrease with depth of both 137Cs and 239+240Pu. In conclusion, about 25% of 137Cs present in the Arctic water and sediments originates from fall- out specific to the area. Another 25% originates from mixing with Atlantic-water from latitudes with higher fall-out. The remaining 50% might originate from European reprocessing facilities. The levels of 241Am in the Svalbard area originate from in situ build-up due to the decay of 241Pu.